Chapter 3
Configuring Your SCXI Hardware and Software
©
National Instruments Corporation
3-25
2.
The SCXI-1122 has one analog configuration jumper for grounding,
shielding, and reference mode selection. Set jumper W1 as shown in
Table 3-18.
Current-Loop Receivers
The SCXI-1122 includes provision for measuring current rather than
voltage. National Instruments offers an SCXI process-current resistor pack,
which consists of four 249
Ω
, 0.1%, 5 ppm, 1/4 W resistors. For more
information on how to install current loop receiver resistors, consult your
SCXI-1122 User Manual.
Scanning Techniques
Note
The SCXI-1122 input multiplexer is composed of relays. Relays have a certain life
expectancy, as listed in Appendix A, Specifications, of the SCXI-1122 User Manual.
To avoid mechanical wear on the relays when the SCXI-1122 is used for
continuous multichannel scanning, you should acquire n samples on a
given channel before proceeding to the next channel, as shown in
Figure 3-3b. For example, rather than performing 100 scans and taking a
single sample from each channel during each scan, as shown in
Figure 3-3a, acquire 100 samples from a channel then switch to the next
channel and acquire a new set of samples, as shown in Figure 3-3b. The
recommended method, software-driven scanning, saves relay life.
Table 3-18.
SCXI-1122 Analog Jumper Configuration
Jumper
Description
Configuration
A-R0R1—Parking position. Use this setting
for MIO or AI devices in DIFF input mode
(factory-default position).
AB-R0— Use this position for DAQ devices
with SE inputs, such as the Lab and 1200
devices, or MIO and AI devices in RSE
mode.
W1
R0 R1 R2
B
A
W1
R0 R1 R2
B
A
W1
